Cationically polymerizable mixtures containing selected metallocene complex salts as curing agents

ABSTRACT

The invention relates to mixtures containing: 
     a) a cationically polymerizable compound and 
     b) a compound of the formula I 
     
         [R.sup.1 (Fe.sup.II R.sup.2).sub.a ].sub.q.sup.⊕an anX.sup.⊖q 
    
      (I) 
     in which a is 1 or 2, n is 1 or 2, R 1  is a substituted or unsubstituted π-arene, R 2  is a substituted or unsubstituted π-arene or cyclopentadienyl anion or indenyl anion, q is an integer from 1 to 3 and X is FSO 3   -   or a q-valent anion of an organic sulfonic acid or of a carboxylic acid; R 1  can also be a polymeric, aromatic ligand. The invention also relates to the novel compounds of the formula I. The curable mixtures can be processed in particular for the production of coatings having a good resistance to heat.

This is a divisional of Ser. No. 08/046,350, filed Apr. 8, 1993, nowU.S. Pat. No. 5,371,259, which is a continuation of Ser. No. 07/759,094,filed Sep. 6, 1991, now abandoned which is a continuation of Ser. No.07/549,518, filed Jul. 6, 1990 now abandoned which is a divisional ofSer. No. 07/202,739 filed Jun. 3, 1988 now U.S. Pat. No. 4,957,946.

The invention relates to cationically polymerizable mixtures containingselected curing agents, novel curing agents for cationicallypolymerizable materials, and activated, polymerizable mixtures and tothe use of these mixtures for the production of coatings.

The use of metallocene complex salts as curing agents for material whichcan be polymerized by cations and/or by free radicals is known per se.

Curable mixtures containing cationically polymerizable materials,preferably epoxide resins, and metallocene complex salts as curingagents are described in EP-A 94,915 and 109,851.

Combinations of material which can be polymerized by cations and/or freeradicals, an iron-arene complex salt and an oxidizing agent are knownfrom EP-A 126,712.

EP-A 152,377 describes combinations of material which can be polymerizedby cations and/or free radicals, selected iron-arene complex salts,sensitizers and, if appropriate, oxidizing agents.

In all these publications complex halides are suggested as anions of themetallocene complex salt. Examples of these are BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻ andSbF₆ ⁻.

Combinations of materials which can be polymerized by free radicals,selected iron-arene complex salts and a photoinitiator of the α-cleavertype are known from EP-A 221,010. According to this text, the anion ofthe iron-arene complex salts is selected from the group consisting ofhalogen, nitrate, sulfate, phosphate, perchlorate or a complex halide.

Problems can occur when mixtures containing solid or highly viscousepoxide resins and metallocene complex salts containing complex metal ornon-metal halide anions are cured, since the curing agents are generallyvery reactive and can produce an inhomogeneous density of crosslinking.This then becomes evident by the formation of bubbles in the curedproduct during the soldering process, and use as a solder-stop lacqueris usually no longer possible. In such cases, therefore, the curingconditions must be controlled very carefully.

Furthermore, there is in the electronics sector a trend towards productscontaining as little as possible free or hydrolysable halogen. It wouldtherefore be desirable if, in addition to curing agents containingcomplex metal or non-metal halide anions from which halogen can be splitoff by hydrolysis, there were also available further compounds which areless sensitive to hydrolysis and have a high reactivity comparable withthat of the previously known curing agents.

High glass transition temperatures in the cured product are demanded fora number of applications; for example when it is used as a solder-stoplacquer, in which good resistance to heat is required. A selected classof curing agents which, in combination with cationically polymerizablecompounds, produce curable mixtures having the advantages mentionedabove have now been found.

The present invention relates to mixtures containing

a) a cationically polymerizable compound and

b) a compound of the formula I

    [R.sup.1 (Fe.sup.II R.sup.2).sub.a ].sub.q.sup.⊕an anX.sup.⊖q (I)

in which a is 1 or 2, n is 1 or 2, R¹ is a substituted or unsubstitutedπ-arene, R² is a substituted or unsubstituted π-arene orcyclopentadienyl anion or indenyl anion, q is an integer from 1 to 3 andX is FSO₃ ⁻ or a q-valent anion of an organic sulfonic acid orcarboxylic acid, subject to the proviso that R¹ can also be a polymeric,aromatic ligand and that in such a case a is a number corresponding tothe average number of complexed groups in the polymer ligand.

Examples of components a) which can be employed within the scope of thisinvention are A) cationically polymerizable, ethylenically unsaturatedcompounds, B) cationically polymerizable, heterocyclic compounds and C)methylol compounds.

Examples of compounds of this type are to be found in EP-A 94,915.

Preferred components a) are cattonically polymerizable, heterocycliccompounds, vinyl esters and vinyl ethers. Divinyl ethers of C₂ -C₁₂aliphatic diols and of polyethylene glycols or polypropylene glycols andalso of dimethylolcyclohexanes are preferred.

Examples of compounds of this type are the divinyl ethers of ethyleneglycol, trimethylene-1,3-diol, 1-methylpropane-1,3-diol,octamethylene-1,8-diol, diethylene glycol, triethylene glycol,tetramethylene-1,4-diol, HO.paren open-st.CH₂ .paren close-st.₂ O.parenopen-st.CH₂ .paren close-st.₄ -O.paren open-st.CH₂ .paren close-st.₂ OHand bis-1,4-methylolcyclohexane.

Components a) which are particularly preferred are epoxide resins, inparticular those containing at least two 1,2-epoxide groups in themolecule. These compounds include, for example, the following:

I) Polyglycidyl and poly-(β-methylglycidyl) esters which can be obtainedby reacting a compound having at least two carboxyl groups in itsmolecule and epichlorohydrin or glycerol dichlorohydrin orβ-methylepichlorohydrin. The reaction is advantageously carried out inthe presence of bases.

Aliphatic polycarboxylic acids can be used as the compound having atleast two carboxyl groups in its molecule. Examples of thesepolycarboxylic acids are oxalic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid ordimerized or trimerized linoleic acid.

It is also possible, however, to employ cycloaliphatic polycarboxylicacids, for example tetrahydrophthalic acid, 4-methyltetrahydrophthalicacid, hexahydrophthalic acid or 4-methylhexahydrophthalic acid.

Aromatic polycarboxylic acids can also be used, for example phthalicacid, isophthalic acid or terephthalic acid.

II) Polyglycidyl or poly-(β-methylglycidyl) ethers which can be obtainedby reacting a compound having at least two free alcoholic hydroxylgroups and/or phenolic hydroxyl groups and a suitably substitutedepichlorohydrin under alkaline conditions or in the presence of an acidcatalyst with subsequent treatment with alkali.

Ethers of this type are derived, for example, from acyclic alcohols,such as ethylene glycol, diethylene glycol and higher poly-(oxyethylene)glycols, propane-1,2-diol or poly-(oxypropylene) glycols,propane-1,3-diol, butane-1,4-diol, poly-(oxytetramethylene) glycols,pentane-1,5-diol, hexane-1,6-diol, hexane-2,4,6-triol, glycerol,1,1,1-trimethylolpropane, pentaerythritol, sorbitol andpolyepichlorohydrins.

They are, however, also derived, for example, from cycloaliphaticalcohols, such as 1,3-dihydroxycyclohexane, 1,4-dihydroxycyclohexane,bis-(4-hydroxycyclohexyl)-methane, 2,2-bis-(4-hydroxycyclohexyl)-propaneor 1,1-bis-(hydroxymethyl)-cyclohex-3-ene.

The epoxide compounds can also be derived from mononuclear phenols, forexample resorcinol or hydroquinone; or they are based on polynuclearphenols, for example bis-(4-hydroxyphenyl)-methane,4,4'-dihydroxybiphenyl, bis-(4-hydroxyphenyl) sulfone,1,1,2,2-tetrakis-(4-hydroxyphenyl)-ethane,2,2-bis-(4-hydroxyphenyl)-propane and2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane and also on novolacs whichcan be obtained by condensing aldehydes, for example formaldehyde,acetaldehyde, chloral or furfuraldehyde, with phenols, such as phenol orphenols which are substituted in the nucleus by chlorine atoms or C₁ -C₉alkyl groups, for example 4-chlorophenol, 2-methylphenol or4-tert-butylphenol, or which can be obtained by condensation withbisphenols as described above.

III) Poly-(S-glycidyl) compounds, in particular di-S-glycidylderivatives derived from dithiols, for example ethane-1,2-dithiol orbis-(4-mercaptomethylphenyl) ether.

IV) Cycloaliphatic epoxide resins, such as bis-(2,3-epoxycyclopentyl)ether, 2,3-epoxycyclopentyl glycidyl ether or1,2-bis-(2,3-epoxycyclopentyloxy)-ethane or 3,4-epoxycyclohexylmethyl3',4'-epoxycyclohexanecarboxylate.

It is also possible, however, to use epoxide resins in which the1,2-epoxide groups are attached to different heteroatoms or functionalgroups; these compounds include, for example, the glycidylether/glycidyl ester of salicylic acid.

If desired, a mixture of epoxide resins can be used in the mixturesaccording to the invention.

Cationically polymerizable compounds which are very particularlypreferred are highly viscous or, in particular, solid epoxide resins,for example solid diglycidyl ethers based on bisphenol or glycidylatedphenol novolacs or cresol novolacs. These are to be understood asmeaning, in general, compounds which, in the uncured state, have a glasstransition temperature higher than 0° C.

Examples of these are solid diglycidyl ethers based on bisphenol F andparticularly on bisphenol A and glycidylated phenol/formaldehydenovolacs or o-cresol/formaldehyde novolacs.

Within the scope of this description π-arene R¹ and R².. is to beunderstood as meaning a π-ligand of the Fe-II central atom, it beingpossible for this ligand to be a carbocyclic-aromatic group or aheterocyclic-aromatic group.

Suitable π-arenes R¹ and R² are, in particular, carbocyclic aromaticgroups having 6 to 24 carbon atoms or heterocyclic-aromatic(heteroaromatic) groups having 3 to 30 carbon atoms, it being possiblefor these groups, if appropriate, to be monosubstituted orpolysubstituted by identical or different monovalent radicals, such ashalogen atoms, preferably chlorine or bromine atoms, or by C₁ -C₈ alkyl,C₁ -C₈ alkoxy, cyano, C₁ -C₈ alkylthio, C₂ -C₆ monocarboxylic acid alkylester, phenyl, C₂ -C₅ -alkanoyl or benzoyl groups. These π-arene groupscan be mononuclear, condensed polynuclear or non-condensed polynuclearsystems, it being possible in the systems last mentioned for the nucleito be attached direct or via bridge members, such as --S-- or --O--.

R² can also be an indenyl anion and, in particular, a cyclopentadienylanton, it being also possible for these anions, if appropriate, to bemonosubstituted or polysubstituted by identical or different monovalentradicals, such as C₁ -C₈ alkyl, C₂ -C₆ monocarboxylic acid alkyl ester,cyano, C₂ -C₅ alkanoyl or benzoyl groups.

In this regard the alkyl, alkoxy, alkylthio, monocarboxylic acid alkylester and alkanoyl substituents can be linear or branched. Typicalalkyl, alkoxy, alkylthio, monocarboxylic acid alkyl ester or alkanoylsubstituents which may be mentioned are methyl, ethyl, n-propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl andn-octyl, methoxy, ethoxy, n-propoxy, tsopropoxy, n-butoxy, n-hexyloxyand n-octyloxy, methylthio, ethylthio, n-propylthio, isopropylthio,n-butylthio, n-pentylthio and n-hexylthio, carboxylic acid methyl,ethyl, n-propyl, isopropyl, n-butyl and n-pentyl esters and acetyl,propionyl, butyryl and valeroyl. In this regard alkyl, alkoxy, alkylthioand monocarboxylic acid alkyl ester groups having 1 to 4, especially 1or 2, carbon atoms in the alkyl moleties and alkanoyl groups having 2 to3 carbon atoms are preferred. Preferred substituted π-arenes orsubstituted indenyl or cyclopentadienyl anions are those containing oneor two of the abovementioned substituents, in particular methyl, ethyl,n-propyl, isopropyl, methoxy or ethoxy groups.

R¹ and R² can be identical or different π-arenes. In addition, R¹ canalso be a polymeric ligand having aromatic radicals.

As an aromatic, polymeric ligand, R¹ is preferably a polymer havingcarbo-cyclic-aromatic radicals. Polystyrene and copolymers ofpolystyrene with butadiene and poly-α-methylstyrene are preferred. Themolecular weights of the polymer ligands vary within the scope of thepolymers customarily obtainable. For polystyrene the molecular weightsare usually between 10⁵ and 10⁶. As a rule, 1-50 mol % of the aromaticgroups, relative to the total number per polymer molecule, are complexedwith Fe^(II). In such cases R² is preferably the cyclopentadienyl anion.The number a corresponds in the case of polymeric ligands to the averagenumber of radicals of a polymer molecule which are complexed by Fe^(II).Preferred ligands R¹ are monomeric π-arenes.

Suitable heteroaromatic π-arenes are, in particular, systems containingone or two S, N and/or O atoms.

Heteroaromatic π-arenes containing one or two S and/or O atoms arepreferred.

Examples of suitable π-arenes are benzene, toluene, xylenes,ethylbenzene, cumene, methoxybenzene, ethoxybenzene, dimethoxybenzene,p-chlorotoluene, m-chlorotoluene, chlorobenzene, bromobenzene,dichlorobenzene, trimethylbenzene, trimethoxybenzene, naphthalene,1,2-dihydronaphthalene, 1,2,3,4-tetrahydronaphthalene,methylnaphthalene, methoxynaphthalene, ethoxynaphthalene,chloronaphthalene, bromonaphthalene, biphenyl, stilbene, indene,4,4'-dimethylbiphenyl, fluorene, phenanthrene, anthracene,9,10-dihydroanthracene, triphenyl, pyrene, perylene, naphthacene,coronene, thiophene, chromene, xanthene, thioxanthene, benzofuran,benzothiophene, naphthothiophene, thianthrene, diphenylene oxide,diphenylene sulfide, acridine and carbazole.

Examples of anions of substituted cyclopentadienes are the anions ofmethylcyclopentadiene, ethylcyclopentadiene, n-propylcyclopentadiene andn-butylcyclopentadiene, and the anions of dimethylcyclopentadiene,methyl cyclopentadienecarboxylate, ethyl cyclopentadienecarboxylate,acetylcyclopentadiene, propionylcyclopentadiene, cyanocyclopentadieneand benzoylcyclopentadiene. Preferred anions are the anion ofunsubstituted indene and, in particular, the anion of unsubstitutedcyclopentadiene.

If a is 2, R² is in each case preferably the substituted orunsubstituted indenyl anion or, in particular, cyclopentadienyl anion.

X.sup.⊖q is FSO₃ ⁻ or, preferably, the q-valent anion of an organicsulfonic acid or carboxylic acid. These are to be understood verygenerally as meaning an aliphatic, cycloaliphatic, carbocyclic-aromatic,heterocyclic-aromatic or araliphatic sulfonic or carboxylic acid.

The anions can be substituted or unsubstituted. Sulfonic or carboxylicacids having a slight nucleophilic character, for example partlyfluorinated or perfluorinated derivatives or derivatives substituted ina position adjacent to the particular acid group, are preferred.

Examples of substituents are halogen, such as chlorine and especiallyfluorine, alkyl, such as methyl, ethyl or n-propyl, or alkoxy, such asmethoxy, ethoxy or n-propoxy.

Examples of aliphatic sulfonic acids are methanesulfonic,ethanesulfonic, n-propanesulfonic, n-butanesulfonic and n-hexanesulfonicacid or the correspondingly partly fluorinated or perfluorinatedderivatives.

Examples of aliphatic carboxylic acids are formic acid, acetic acid,propionic acid, butyric acid, pivalic acid, caproic acid,2-ethylhexylcarboxylic acid, and fatty acids, such as lauric acid,myristic acid or stearic acid, and also the partly fluorinated orperfluorinated derivatives of these acids.

Examples of cycloaliphatic sulfonic or carboxylic acids arecyclohexanesulfonic acid, cyclohexanecarboxylic acid,camphor-10-sulfonic acid or the partly fluorinated or perfluorinatedderivatives thereof.

Examples of carbocyclic-aromatic sulfonic acids are benzenesulfonic,toluenesulfonic, ethylbenzenesulfonic, isopropylbenzenesulfonic,dodecylbenzenesulfonic or dimethylbenzenesulfonic acid,2,4,6-triisopropylbenzenesulfonic acid, 2,4,6-trimethylbenzenesulfonicacid, naphthalenesulfonic acid, naphthalenedisulfonic acids ornaphthalenetrisulfonic acids and the corresponding alkylated or partlyfluorinated or perfluorinated derivatives of these sulfonic acids.

Examples of heterocyclic-aromatic sulfonic acids are pyridinesulfonic,thiophenesulfonic or pyrrolesulfonic acid and the corresponding partlyfluorinated or perfluorinated derivatives of these acids.

Examples of araliphatic sulfonic acids are benzylsulfonic acid,α-methylbenzylsulfonic acid and the corresponding partly fluorinated orperfluorinated derivatives of these compounds.

Examples of carbocyclic-aromatic carboxylic acids are benzoic acid,toluenecarboxylic, ethylbenzenecarboxylic, isopropylbenzenecarboxylic ordimethylbenzenecarboxylic acid, naphthalenecarboxylic acid oranthracenecarboxylic acid and the corresponding partly fluorinated orperfluorinated derivatives of these compounds.

Examples of heterocyclic-aromatic carboxylic acids arepyridinecarboxylic, thiophenecarboxylic or pyrrolecarboxylic acid andthe corresponding partly fluorinated or perfluorinated derivatives ofthese compounds.

Examples of araliphatic carboxylic acids are benzylcarboxylic acid,α-methylbenzylcarboxylic acid and cinnamic acid, and also thecorresponding partly fluorinated or perfluorinated derivatives of thesecompounds.

X.sup.⊖q is preferably the monovalent anion of an organic sulfonic acid,especially a partly fluorinated or perfluorinated sulfonic acid. Theseanions are distinguished by a particularly slight nucleophiliccharacter.

Preferred mixtures are those in which component b) is a compound of theformula I and X.sup.⊖q is a monovalent anion of an aliphatic, partlyfluorinated aliphatic or perfluorinated alphatic sulfonic acid or of anaromatic, partly fluorinated aromatic or perfluorinated aromaticsulfonic acid.

Mixtures in which component b) is a compound of the formula I andX.sup.⊖q is selected from the group consisting of CF₃ SO₃ ⁻, C₂ F₅ SO₃⁻, n-C₃ F₇ SO₃ ⁻ n-C₄ F₉ SO₃ ⁻, n-C₄ F₉ SO₃ ⁻, n-C₆ F₁₃ SO₃ ⁻, n-C₈ F₁₇SO₃ ⁻ and C₆ F₅ SO₃ ⁻ are particularly preferred.

Curable mixtures containing, as the component b) a compound of theformula Ia

    [R.sup.1 Fe.sup.II R.sup.2 ].sup.⊕n nX.sup.⊖   (Ia)

in which R¹ is a π-arene, R² is a π-arene or a cyclopentadienyl anion, nis as defined above and X⁻ is an anion of an organic sulfonic acid arepreferred.

Curable mixtures which are particularly preferred, contain, as thecomponent b), a compound of the formula I or Ia in which R¹ is selectedfrom the group consisting of toluene, xylene, ethylbenzene, cumene,methoxybenzene, methylnaphthalene, methoxynaphthalene, pyrene, perylene,stilbene, diphenylene oxide and diphenylene sulfide, R² is acyclopentadienyl anion and X⁻ is a perfluoroalkylsulfonate orperfluorophenylsulfonate.

Other preferred mixtures contain, as the component a), a solid epoxideresin and, as the component b), a compound of the formula Ia in which R¹is selected from the group consisting of toluene, xylene, ethylbenzene,cumene, methoxybenzene, methylnaphthalene, methoxynaphthalene, pyrene,perylene, stilbene, diphenylene oxide and diphenylene sulfide, R² is acyclopentadienyl anion and X.sup.⊖ is a perfluoroalkylsulfonate or aperfluorophenylsulfonate, but particularly a trifluoromethanesulfonateor a nonafluorobutanesulfonate.

With the exception of 1,4-dimethylbenzene-cyclopentadienyl-iron-(II)trifluoromethanesulfonate and9,9-dimethylfluorene-cyclopentadienyl-iron-(II) fluosulfonate, thecompounds of the formula I are novel. The previously known compounds aredescribed in Inorg. Chem. 22, 4047 (1983) and 23, 2633 (1984) and inNouv. J. Chim. 8(6), 381 (1984). These publications describe thephotolyrically induced ligand exchange reaction at iron-arene complexesand the preparation of the compounds, but not their use as curing agentsfor cationically polymerizable materials.

The invention therefore also relates to the compounds of the formula I,with the exception of 1,4-dimethylbenzene-cyclopentadienyl-iron-(II)trifluoromethanesulfonate and9,9-dimethylfluorene-cyclopentadienyliron(II) fluosulfonate.

The following are examples of particularly preferred compounds:(toluene) (cyclopentadienyl)-iron(II) trifluoromethanesulfonate,(ethylbenzene) (cyclopentadienyl)-iron(II) trifluoromethanesulfonate,(cumene)-(cyclopentadienyl)-iron(II) trifluoromethanesulfonate,(methoxybenzene)-(cyclopentadienyl)-iron(II) trifluoromethanesulfonate,(methylnaphthalene)-(cyclopentadienyl)-iron(II)trifluoromethanesulfonate, (methoxynapthalene)(cyclopentadienyl)-iron(II) trifluoromethanesulfonate,(pyrene)(cyclopentadienyl)-iron(II) trifluoromethanesulfonate,(perylene)(cyclopentadienyl)-iron(II) trifluoromethanesulfonate,(stilbene)(cyclopentadienyl-iron)(II) trifluoromethanesulfonate,(diphenylene oxide)(cyclopentadienyl)-iron(II)trifluoromethanesulfonate,(diphenylene sulfide)(cyclopentadienyl-iron(II)trifluoromethanesulfonate, (fluorene)(cyclopentadienyl)-iron(II)trifluoromethanesulfonate, and the correspondingnonofluorobutanesulfonates, tridecafluorohexanesulfonates,heptadecafluorooctanesulfonates, fluosulfonates,pentafluorophenylsulfonates and trifluoroacetates.

The materials employed as the component a) are known per se and are forthe most part commercially available.

The compounds of the formula I are prepared analogously to knownprocesses. The preparation of metallocene complexes of this type havingcomplex halide anions is described, for example, in EP-A 94,915.

As a variation from the processes described therein, the compounds ofthe formula I can be prepared by introducing in a manner known per se ananion of the acid H_(q) X instead of an anion of a complex halide; inthis formula q and X are as defined earlier in the text.

The introduction of the anion can be effected, for example, by reactinga metallocene halide with an acid H_(q) X or with a dissolved salt ofsuch an acid.

The curable mixtures according to the invention are sensitive to light.They can be obtained in any desired form, for example as homogeneousliquid mixtures or in a homogeneous or inhomogeneous form. Homogeneousproducts can be obtained in a manner known per se, for example byliquefying solid polymerizable organic materials, if appropriate withthe addition of suitable solvents in the dark or under red light,heating the materials to temperatures above their glass transitionpoint, adding the initiator of the formula I and cooling the resultingmixtures. If desired, the products thus obtained can subsequently becomminuted. Inhomogeneous products can be obtained, for example, bymixing polymerizable materials in the form of powder with initiatorsaccording to the invention.

The curable mixtures according to the invention can be stored at roomtemperature for a considerable time in comparative darkness, for examplein red light.

Depending on their composition and their end use, for example for theproduction of coatings or films, they can be cured by the directapplication of heat. As a rule, the direct curing by heat is carried outat temperatures of 130°-220° C., in particular 150°-180° C. Thetemperatures for direct curing by heat are preferably close to thedecomposition point of the initiator employed. It is preferable toemploy initiators of the formula I in which R¹ is a condensed aromatichydrocarbon in the direct curing by heat. Curing by heat is normallycomplete after about 3 to 10 minutes.

As used here, the expression "cure" means the conversion of the soluble,either liquid or meltable, cationically polymerizable compound intosolid, insoluble and infusible, three-dimensionally crosslinkedproducts. This is effected, as a rule, with simultaneous shaping to giveshaped articles, impregnations, coatings or adhesive joints.

Two-stage polymerization (curing) is particularly preferred and iseffected by first activating the initiator of the formula I byirradiating the curable mixture with actinic light and then curing byheat the resulting activated precursors, the temperature of irradiationbeing below the temperature used for the subsequent curing by heat.These activated precursors can normally be cured at temperatures whichare considerably lower than the temperature required in the case ofdirect curing by heat, and are advantageously within the range from 80°to 180° C., preferably from 100° to 180° C. This two-stage curing alsomakes it possible to control the polymerization in a particularly simpleand advantageous manner. In addition, the activated precursorsobtainable from the curable mixtures according to the invention can bestored for a considerable time at room temperature, even in light, thisapplying particularly to mixtures containing a highly viscous or solidepoxide resin as the component a) . This characteristic constitutes afurther substantial advantage of two-stage curing and of these activatedprecursors. In general, activated precursors obtainable from liquidcurable mixtures according to the invention have only a limitedstability on storage in light and are advantageously processed furtherimmediately.

The irradiation of the curable mixtures for the preparation of theactivated precursors is advantageously effected by means of actiniclight, preferably light of a wavelength from 200 to 600 nm. Examples ofsuitable light sources are xenon lamps, argon lamps, tungsten lamps,carbon arcs, metal halide lamps and metal arc lamps, such aslow-pressure, medium-pressure and high-pressure mercury vapour lamps, orlasers, such as argon or krypton ion lasers. Irradiation is preferablycarried out using metal halide lamps or high-pressure mercury vapourlamps and also with argon or krypton ion lasers. The irradiation timedepends on various factors, including, for example, the polymerizableorganic material, the nature of the light source and the distance of thelatter from the irradiated material. The irradiation time is preferably10 to 60 seconds.

The heating of the exposed compositions can be carried out inconventional convection ovens. If short heating or reaction times arenecessary, the heating can be carried out by exposure to, for example,IR radiation, IR lasers or microwave devices.

In general, the curing temperature in direct curing by heat or in thethermal stage of two-stage polymerization is higher than that ofmixtures containing the corresponding metallocene initiators havinganions of complex metal or non-metal halides.

Although the curing agents of the formula I in the epoxide matrix are,as a rule, thus less reactive, in general a cured product is formedwhich has a higher glass transition temperature than when curing iscarried out using the metallocene complexes containing complex halideanions.

Accordingly, the invention also relates to the cured product obtainableby i) the direct curing by heat of the curable mixture, as definedabove, or ii) two-stage polymerization of the curable mixture, asdefined above.

The invention also relates to activated, curable mixtures which areobtainable by irradiating with actinic light curable mixtures containinga cationically polymerizable organic material a) and at least onecompound of the formula I at a temperature which is below thetemperatures used for the subsequent curing by heat. What has beenstated above in respect of the preferred cationically polymerizablematerials and compounds of the formula I also applies here.

The curable mixtures and the activated precursors obtainable therefromcan also contain further additives which are known and are customarilyemployed in the technology of photopolymerizable materials.

Examples of such additives are pigments, dyes, fillers and reinforcingagents, such as glass fibres and other fibres, fire-retardingsubstances, antistatic agents, flow control agents, antioxidants andlight stabilizers.

The mixtures according to the invention can, of course, also containcombinations of initiators of the formula I and sensitizers.Particularly in the case of compounds of the formula I in which R¹ is asubstituted or unsubstituted benzene derivative an increase in thesensitivity to light is usually observed when sensitizers are added.Examples of suitable sensitizers are to be found in EP-A 152,377.Furthermore, combinations of initiators of the formula I, oxidizingagents and, if appropriate, sensitizers for the compounds I can also beemployed in the mixtures according to the invention. As a rule,oxidizing agents reduce the curing temperatures and permit processingunder mild conditions. Suitable oxidizing agents are mentioned in EP-A126,712.

In order to increase their stability on storage in the dark, the curablemixtures and activated precursors can contain weak organic bases, suchas nitriles, tertiary amines or urea derivatives. In order to preventpremature reaction caused by unintended exposure to light, small amountsof UV absorbants and/or organic dyes can be added.

The curable mixtures according to the invention and the activatedprecursors obtainable therefrom are preferentially suitable for theproduction of surface coatings on a variety of substrates.

It is very particularly preferred to use the curable mixtures havinghighly viscous or solid epoxide resins as the component a). In thisembodiment the curable mixtures are preferably used as solder-stopmasks. The present invention also relates to these uses.

Examples of suitable substrates are metals, such as aluminium, steel,cadmium, zinc and, preferably, copper, semi-conductors, such as silicon,germanium or GaAs, ceramics, glass, plastics, paper or wood andespecially metal-coated laminates such as are used for the production ofprinted circuit boards.

If initially only part of the coating is exposed imagewise in thetwo-stage polymerization described above, for example if it isirradiated through a mask, the unexposed areas can, after a subsequentbrief curing by heat, be removed by means of a suitable solvent. Thecurable mixture according to the invention are thus suitable for thereproduction of images or for the production of printing plates andespecially printed circuits (photoresists) by methods known per se (see,for example, British Patent Specification 1,495,746).

If, in the production of images, the light energy is minimized duringthe photostructuring, for example in the production of solder-stop masksby exposure to lasers, a multi-stage curing process can be recommended.In this process, the first step is the production of a structure, in thecourse of which the lowest possible radiation intensity can be employed,and subsequently this structure is subjected to after-treatment in orderto improve its final properties.

The process comprises the following steps:

A) imagewise exposure to actinic light of a substrate coated with thecomposition according to the invention,

B) heat-treating the system at an elevated temperature so thatpreliminary curing takes place in the irradiated portions of thesurface,

C) developing the system by treatment with a solvent so that theprecured composition in the irradiated portions of the surfacesubstantially remains on the substrate and is dissolved away in thenon-irradiated portions of the surface,

D) exposing the whole of the surface to actinic light, and

E) subsequent heat treatment in order to complete the curing of theprecured product.

The temperatures in steps B) and E) are preferably above 130° C. and thecuring times in these steps are preferably more than 10 minutes in thecase of step B) and more than 15 minutes in the case of step E). Theradiation dosage in stage A) is preferably such that, in combinationwith step B), an adequate precuring just takes place, so that stage C)can be carried out without problems. The individual parameters in thiscombination can be determined by those skilled in the art by means ofroutine tests.

The mixtures according to the invention and the activated precursorsobtainable therefrom can also be used as adhesives or for the productionof putties, fillers or fibre-reinforced composite materials andlaminated articles.

For the above applications, the curable compositions according to theinvention or the activated precursors obtainable therefromadvantageously contain 0.1 to 15% by weight, preferably 0.5 to 5% byweight, relative to the polymerizable organic material a), of at leastone compound of the formula I.

The following examples illustrate the invention.

A) Preparation of the Curing Initiators EXAMPLE 1 (η⁶ Cumene)(η⁵-cyclopentadienyl)-iron(II) trifluoromethanesulfonate

A mixture of 7.5 g of ferrocene, 0.27 g of aluminium, 5.4 g of aluminiumchloride and 4.5 g of titanium tetrachloride in 35 ml of cumene isstirred for 2 hours at 100° C. The mixture is cooled to room temperatureand poured into 20 ml of 32% hydrochloric acid/100 g of ice, stirred for2 hours and then filtered. The aqueous, yellow-brown phase is separatedoff and 6 g of trifluoromethanesulfonic acid are added to it. Theproduct is extracted with twice 50 ml of methylene chloride, themethylene chloride solution is washed once with 30 ml of 10% sodiumbicarbonate solution and once with 50 ml of water, dried by adding 5 gof sodium sulfate, and filtered, and the methylene chloride is removedby evaporation. Recrystallization from methylene chloride/hexane affords12.25 g (78.5% of theory) of the abovementioned complex: melting point49° C.

EXAMPLE 2 (η⁶ -Cumene) (η⁵ -cyclopentadienyl)-iron(II)nonafluorobutanesulfonate

Prepared by the method described in Example 1, but employing 13.5 g ofpotassium nonafluorobutanesulfonate instead of trifluoromethanesulfonicacid. This gives 16.6 g (77% of theory) of the abovementioned complex:melting point 45.5° C.

EXAMPLE 3 (η⁶ -Cumene) (η⁵ -cyclopentadienyl)-iron(II)pentafluorobenzenesulfonate

Prepared by the method described in Example 1, but employing 10.8 g ofsodium pentafluorobenzenesulfonate instead of trifluoromethanesulfonicacid. This gives 12.7 g (65% of theory) of the abovementioned complex:melting point 122° C.

EXAMPLE 4 (η⁶ -Cumene) (η⁵ -cyclopentadienyl)-iron(II) trifluoroacetate

Prepared by the method described in Example 1, but employing 5.4 g ofsodium trifluoroacetate instead of trifluoromethanesulfonic acid. Thisgives 9.7 g (68.5% of theory) of the abovementioned complex in the formof a dark brown oil having a decomposition point above 210° C.

EXAMPLE 5 (η⁶ -Stilbene) (η⁵ -cyclopentadienyl)-iron(II)trifluoromethane-sulfonate

A solution of 10 g of (η⁶ -stilbene) (η⁵ -cyclopentadienyl)-iron(II)hexafluorophosphate¹ and 3 g of aluminium chloride in 100 ml ofmethylene chloride is stirred under nitrogen for 1 hour. After 160 ml ofwater have been added the mixture is stirred for a further 30 minutesand the aqueous phase is then separated off in a separating funnel and3.66 g of trifluoromethanesulfonic acid are added dropwise slowly. Theprecipitate formed is filtered off, rinsed with a little water and driedin vacuo at 50° C. This gives 4.24 g (42% of theory) of theabovementioned complex: melting point: 130° C.

EXAMPLE 6 (η⁶ -Stilbene) (η⁵ -cyclopentadienyl)-iron(II)4-toluenesulfonate

Prepared by the method described in Example 5, but employing 4.3 g of4-toluenesulfonic acid instead of trifluoromethanesulfonic acid. Thisgives 3.64 g (34.4% of theory) of the abovementioned complex: meltingpoint: 136° C.

EXAMPLE 7 (η⁶ -1-Methylnaphthalene) (η⁵ -cyclopentadienyl)-iron(II)trifluoromethanesulfonate

Prepared by the method described in Example 1, but employing 35 ml of1-methylnaphthalene instead of cumene. This gives 10.8 g (72% of theory)of the abovementioned complex: melting point 78° C.

B) Use Examples Examples I-III General Working Instructions

Solutions consisting of 100 g of technical epoxide cresol novolac(epoxide value 4.5 equivalents/kg), 50 g of a technical bisphenol Adiglycidyl ether (epoxide value 0.35 equivalents/kg), 30 g of talc(Cyprus), 2 g of Irgalithgrun (Ciba-Geigy), 180 g of cyclohexanone andthe amount of photoinitiator (iron-arene complex) and sensitizerindicated in Table 1 are applied to a printed circuit board by means ofa 100μ wire doctor-blade. The film, which is initially wet, is dried at80° C. The board thus produced is exposed to a 5000-watt high-pressuremercury vapour lamp at a distance of 50 cm from the mask laid on it. Theexposure time is 1 minute. The board is then precured for 10 minutes at110° C. Development is carried out in cyclohexanone, the non-exposedportions (soldering lugs) are dissolved. The board is then post-curedfor 30 minutes at 135° C. After being coated with flux, the board isfinally immersed for 10 seconds in a bath of solder (lead-tin) heated to270° C. and is then inspected (cf. Table 1).

Examples IV-VIII General Working Instructions

Solutions according to Examples I-III and Table 2 are applied to copperfoils 70μ thick by means of a 100μ wire doctor-blade. The film is driedfor 30 minutes at 80° C. and is then exposed for 1 minute (see ExamplesI-III) and cured for 1 hour at 135° C.

The glass transition temperatures of the layers thus obtained aredetermined by thermomechanical analysis (Mettler, TMA 40 measuring cell)(cf. Table 2).

                                      TABLE 1                                     __________________________________________________________________________                      Photoinitiator    Sensitizer                                                                           Appearance                         Ex-               concentration     concentration                                                                        after solder                       ample                                                                             Photoinitiator*.sup.)                                                                       [mmol] Sensitizer [mmol] bath                               __________________________________________________________________________    I   [Cumene Fe Cp] CF.sub.3 SO.sub.3                                                            10     Isopropylthioxanthone                                                                    5      No change                          II  [Cumene Fe Cp] C.sub.4 F.sub.9 SO.sub.3                                                     10     Isopropylthioxanthone                                                                    5      No change                          III [Stilbene Fe Cp] CF.sub.3 SO.sub.3                                                          10     --         --     No change                          __________________________________________________________________________     *.sup.) Cp = cyclopentadienyl anion                                      

                                      TABLE 2                                     __________________________________________________________________________                       Photoinitiator    Sensitizer                               Ex-                concentration     concentration                            ample                                                                             Photoinitiator*.sup.)                                                                        [mmol] Sensitizer [mmol] Tg (°C.)                   __________________________________________________________________________    IV  [Cumene Fe CP] CF.sub.3 SO.sub.3                                                             10     Isopropylthioxanthone                                                                    5      137                               V   [Cumene Fe Cp] C.sub.4 F.sub.9 SO.sub.3                                                      10     Isopropylthioxanthone                                                                    5      140                               VI  [Cumene Fe Cp] C.sub.6 F.sub.5 SO.sub.3                                                      10     Isopropylthioxanthone                                                                    5      162                               VII [Stilbene Fe CP] CF.sub.3 SO.sub.3                                                           10     --         --     143                               VIII                                                                              [Naphthalene Fe Cp] CF.sub.3 SO.sub.3                                                        10     --         --     140                               __________________________________________________________________________

What is claimed is:
 1. A cured product obtained(i) by the direct curingby heat of a curable mixture which comprises (a) an epoxy resin, a vinylether or a vinyl ester, and (b) a compound of formula Ia

    [R.sup.1 Fe.sup.II R.sup.2 ].sup.+n nX.sup.-               (Ia)

in which n is 1 or 2, R¹ is a π-arene, selected from the groupconsisting of toluene, xylene, ethylbenzene, cumene, methoxybenzene,methylnaphthalene, methoxynaphthalene, pyrene, perylene, stilbene,diphenylene oxide and diphenylene sulfide, R² is a cyclopentadienylanion, and X⁻ is an anion of a carbocyclic aromatic or heterocyclicaromatic sulfonic acid selected from the group consisting ofbenzenesulfonic, tolenesulfonic, ethylbenzenesulfonic,isopropylbenzenesulfonic, dodecylbenzenesulfonic ordimethylbenzenesulfonic acid, 2,4,6-triisopropylbenzenesulfonic acid,2,4,6-trimethylbenzenesulfonic acid, naphthalenesulfonic acid,naphthalenedisulfonic acid, and naphthalenetrisulfonic acid, and thecorresponding alkylated or partly fluorinated or perfluorinatedderivatives thereof; pyridinesulfonic, thiophenesulfonic, andpyrrolesulfonic acid and the corresponding partly fluorinated orperfluorinated derivatives of these acids; or (ii) by irradiating acurable mixture, described above, with actinic light and subsequentlycuring by heat, the irradiation temperature being below that used forthe subsequent curing by heat.
 2. A product according to claim 1 whereincomponent (a) is a highly viscous or solid epoxide resin.
 3. A productaccording to claim 1 wherein component (a) is a solid epoxide resin.